The development of technical solutions for the temporary in situ containment and management of soils containing recalcitrant heavy hydrocarbons (RHH) or other contamination promises an exceptionally high return-on-investment. Attributes of an ideal in situ delivery strategy (ISDS), here defined as methods and processes for in situ containment and management of shallow impacted soils include: (i) effective, custom-designed (short or long-term) containment of contaminants at shallow depths of 30 ft. or less; (ii) compatibility with a wide range of applications; (iii) easy installation; (iv) easy removal if temporary; (v) economical installation; (vi) acceptability to all stakeholders of contaminated sites.
Successful, engineered solutions to horizontal contaminant transport exist, but in situ vertical containment is more difficult to achieve. While horizontal barriers such as the sheet pilings or slurry walls commonly used in the industry are a cost-effective reliable and proven means of lateral containment of contaminants, water, and treatment agents in soil, there is no counterpart barrier available for vertical containment of contaminants, i.e., downward migration of pollutants to deeper soil layers that are in hydraulic communication with groundwater serving as a potential drinking water resource. This technology gap limits complete isolation of contaminants for in situ treatment, thereby reducing the effectiveness of some soil and groundwater remediation efforts.
Possible solutions for creating a horizontal barrier in situ have been proposed in the literature, but technical challenges remain. Soil improvement methods such as biopolymer and bentonite admixture, augmentation of bacterial growth (e.g., biofilm growth), soil freezing, and calcite precipitation may be viable tools for reducing the hydraulic conductivity of the soil to create a temporary, removable, horizontal barrier in situ. However, an additional challenge with most of these methods is creating a continuous horizontal barrier for combined in situ containment and control for predefined periods of time.
Prior work has established that in situ soil containment is challenging. It is estimated that vertical containment has to provide 98% coverage of the plan area or better in order to arrive at an acceptable technical solution for a typical environmental remediation project (Kavazanjian, 2013). Vertical and horizontal continuity of treatment is a function of the type and quantity of agent used as well as the hydraulic conductivity characteristics (magnitude and vertical and lateral distribution) of the treated soil. Prior work has identified soil freezing as a potential solution that also provides the desirable aspect of barrier temporality (McCauley et al., 2002; Andersland et al., 1996a; Andersland et al., 1996b; Dash, 1991; Tumeo and Davidson, 1993); however, the effectiveness of the soil freezing approach is dependent on the saturation level of the soil, which ideally should be near 100%. The modification of clay properties by chemical agents also has been established as a method for horizontal barrier formation (Liu et al., 2013; Mosavat et al. 2013).
The lateral dispersion of agents injected to achieve containment is difficult to estimate from theory and is known to be highly non-uniform in practice. In addition to the challenge of regulating the spatial aspect of barrier formation, temporal dynamics also are difficult to predict (Chen-Charpentier and Kojouharov, 2001; Chen and Kojouharov, 1999; Komlos et al., 1998).
A few previous studies have examined the performance of potential barrier materials under different groundwater, pressure, soil chemistry, and microbiologic regimes (e.g., McCauley et al., 2002; Andersland et al., 1996a; Andersland et al., 1996b; Dash, 1991; Fall et al. 2009; Tumeo and Davidson, 1993). However, a comprehensive evaluation of promising in situ isolation and treatment methods-simulated in tandem, is lacking.
Thus, there is a clear need for (1) screening temporal horizontal barrier formation methods for effectiveness; (2) characterizing the interactions between in situ isolation and treatment technologies; and (3) evaluating the performance of these coupled systems in situ at a scale relevant and realistic for use at RHH impacted sites. The primary technical barrier that needs to be addressed is construction of a horizontal containment barrier in the subsurface, including selection of appropriate environmentally friendly soil-cementation material and formation of a continuous horizontal barrier. If this method is used in conjunction with applications requiring flushing of the soil volume, the barrier may constitute any form of hydraulic control to capture, contain, collect, or recirculate the liquids above it.
An additional technical barrier is the need, or at least desire, in many situations for the vertical barrier to be temporary, i.e. to restore the ground to its pre-containment condition. This may be necessary or desirable to mitigate the potential for long term impacts to groundwater systems, e.g. to restore recharge to an underlying aquifer via infiltration and percolation of precipitation.
Thus, the present invention provides novel solutions for the deficiencies inherent in systems like those described above. Disclosed herein is a new and long sought technical solution for creating a low-permeability horizontal barrier that will connect with the lower ends of a vertical barrier system to establish the desired in situ containment or control of a soil volume. The systems and methods of the present invention allow various soil-treatment applications to be executed on site without the need for excavation and off-site transport of soils.